I don't understand.

I don't understand what is wrong with me. When I test out a combo either I like or heard from a youtuber like LeftSpinBeys against Wizard Rod 3-60 B and/or Dran Buster 1-60 LF and works out. But when I test it out more and/or take it to a tournament, it just doesn't work as well as I hoped. The only combos that worked for me was Silver Wolf 3-60 H, which is a meta bey and I want to stray away from that as far as possible and sometimes Samurai Saber 5-60 P, something only meant to counter Cobalt Dragoon on Elevate which turned out to be a somewhat good balance type. Does anyone have any possible explanations on why most of my combos do worse in real tournaments than in practice?
Are you practicing by yourself or are you practicing with a friend? 1 player and 2 player testing tends to yield pretty different results in X due to how incredibly important launch tech and timing is this gen.
Just by myself, with one String launcher since that is the easiest for me at the moment.